1. Field of the Invention
The present invention relates to surface acoustic wave devices including a scandium-containing aluminum nitride film defining a piezoelectric member.
2. Description of the Related Art
As mobile communication apparatuses have come to operate at higher frequencies in recent years, surface acoustic wave devices used in those communication apparatuses are required to operate at higher frequencies as well.
High Performance Surface Acoustic Resonators in SHF Range Using ScAlN/6H-SiC Structure (Piezoelectric Material & Devices Symposium 2012, pp. 43-46) discloses a surface acoustic wave device in which a ScAlN thin film and an interdigital transducer (IDT) electrode are formed on a SiC or diamond substrate. The ScAlN thin film is an AlN thin film in which Sc is doped. It is considered that piezoelectricity can be raised by increasing a concentration of Sc.
High Performance Surface Acoustic Resonators in SHF Range Using ScAlN/6H-SiC Structure (Piezoelectric Material & Devices Symposium 2012, pp. 43-46) discloses that, because of a ScAlN thin film being excellent in piezoelectricity, a surface acoustic wave device having a wide frequency band as well as having a high Q value can be obtained. In High Performance Surface Acoustic Resonators in SHF Range Using ScAlN/6H-SiC Structure (Piezoelectric Material & Devices Symposium 2012, pp. 43-46), in order to achieve a higher frequency operation, a high acoustic velocity substrate made of diamond or SiC is used. However, a substrate of diamond is expensive. Meanwhile, in the case where a substrate of SiC is used, the substrate need have high electric resistivity. However, a SiC substrate with high electric resistivity is hard to obtain. Even if such substrate is obtained, its price is extremely high.